Brisbane’s average rainfall is around 1200 mm. a year. Of course, rainfall patterns vary across the large metropolitan area.

The pattern is for a dry period from April to September, which receives only around 400 mm., with a wet season from October to March getting twice as much rain- about 800 mm.

Here’s how to calculate how much water you can collect from your roof.

Take the number of square metres of roof, muliply by the number of millimetres of rainfall, to give the number of litres. e.g. If you have 150 square metres of roof, and the average Brisbane rainfall is 1200 mm, then you could collect over 180,000 litres a year.

A 10mm rainfall would yield 1500 litres! In both cases, it’s safest to subtract 10% to allow for absorbtion, evaporation etc.

For your information, here is the official Brisbane monthly average rainfall graph, together with the average number of rain days, supplied by the Bureau of Meteorology.

If you live in Brisbane (or elsewhere in Queensland), we’d like to help you with your water tank requirements. Learn more at our Brisbane Water Tanks page.